This invention relates generally to multilayer reflectors, and more particularly multilayer dielectric reflectors having selective transmission.
Multilayer dielectric reflectors are often used to partition portions of the electromagnetic spectra between reflection and transmission. Multilayer dielectric reflectors typically employ a number of layers of at least two different materials within an optical stack. The different materials have refractive indices along at least one in-plane axis of the stack that are sufficiently different to substantially reflect light at the interface of the layers. Typical dielectric reflectors have very little absorption. Depending on its intended use, a dielectric stack can be constructed to reflect large areas of the electromagnetic spectrum, specific portions thereof, one polarization of light, etc. They can also be constructed to reflect light incident at normal and/or glancing angles of incidence.
One type of multilayer dielectric reflector is formed by sequentially depositing thin films on a substrate. Using this approach, the thickness of each individual layer can be carefully controlled to obtain a desired reflection band profile. An alternative approach to forming a dielectric reflector uses coextruded polymeric layers to form an optical stack. In each type of reflector, using more layers tends to improve the performance of the resulting dielectric reflector.